658 research outputs found
An introduction to NASA's turbine engine hot section technology (HOST) project
An overview of research to develop and improve the accuracy of current analysis methods so that increased durability can be designed into future engines is presented. Emphasis is placed on improved accuracy in life prediction. Component design, including description of the thermal and aerodynamic environments, the material's mechanical response, the interactions between environmental and structural response, and high temperature instrumentation capable of measuring near-engine environment effects are addressed. Component tests, improved modeling of the physical phenomena, and tests to verify the proved models are also discussed
Controlling Fairness and Bias in Dynamic Learning-to-Rank
Rankings are the primary interface through which many online platforms match
users to items (e.g. news, products, music, video). In these two-sided markets,
not only the users draw utility from the rankings, but the rankings also
determine the utility (e.g. exposure, revenue) for the item providers (e.g.
publishers, sellers, artists, studios). It has already been noted that
myopically optimizing utility to the users, as done by virtually all
learning-to-rank algorithms, can be unfair to the item providers. We,
therefore, present a learning-to-rank approach for explicitly enforcing
merit-based fairness guarantees to groups of items (e.g. articles by the same
publisher, tracks by the same artist). In particular, we propose a learning
algorithm that ensures notions of amortized group fairness, while
simultaneously learning the ranking function from implicit feedback data. The
algorithm takes the form of a controller that integrates unbiased estimators
for both fairness and utility, dynamically adapting both as more data becomes
available. In addition to its rigorous theoretical foundation and convergence
guarantees, we find empirically that the algorithm is highly practical and
robust.Comment: First two authors contributed equally. In Proceedings of the 43rd
International ACM SIGIR Conference on Research and Development in Information
Retrieval 202
Proton Nuclear Magnetic Resonance Investigation of the [2Fe-2S]\u3csup\u3e1-\u3c/sup\u3e-Containing “Rieske-Type” Protein from \u3cem\u3eXanthobacter\u3c/em\u3e Strain Py2
Proton NMR spectra of the Rieske-type ferredoxin from Xanthobacter strain Py2 were recorded in both H2O and D2O buffered solutions at pH 7.2. Several well-resolved hyperfine-shifted 1H NMR signals were observed in the 90 to −20 ppm chemical shift range. Comparison of spectra recorded in H2O and D2O buffered solutions indicated that the signals at −11.4 (L) and −15.5 (M) ppm were solvent-exchangeable and thus were assigned to the two histidine Nε2H protons. The remaining observed signals were assigned based upon chemical shift, T1 values, and one-dimensional nuclear Overhauser effect (nOe) saturation transfer experiments to either CβH or CαH protons of cluster cysteinyl or histidine ligands. Upon oxidation of the [2Fe-2S] cluster, only two broad resonances were observed, indicating that the two Fe(III) ions are strongly antiferromagnetically coupled. In addition, the temperature dependence of each observed hyperfine-shifted signal in the reduced state was determined, providing information about the magnetic properties of the [2Fe-2S]1- cluster. Fits of the temperature data observed for each resonance to equations describing the hyperfine shift with their Boltzmann weighting factors provided a ΔEL value of 185 ± 26 cm-1 which, in turn, gives −2J as 124 cm-1. These data indicate that the two iron centers in the reduced [2Fe-2S] Rieske-type center are moderately antiferromagnetically coupled. The combination of these data with the available spectroscopic and crystallographic results for Rieske-type proteins has provided new insights into the role of the Rieske-type protein from Xanthobacter strain Py2 in alkene oxidation
Mule Deer Management in Southeastern Montana
In 1982, Montana Fish, Wildlife and Parks Region 7 implemented a five week regionwide general license either-sex plus additional antlerless B license harvest structure for mule deer (Odocoileus hemionus). This harvest strategy implemented three important changes from previous years. First, the regionwide harvest structure eliminated the use of small hunting districts and allows the law of diminishing returns to operate: hunters tend to avoid areas with low deer numbers and focus on areas with higher densities. Second, general licenses were made either-sex, rather than antlered-only for mule deer. Third, following natural population declines (e.g., due to severe natural stressors), biologists began increasing antlerless quotas soon after populations began to recover, rather than waiting until populations were at or above long-term averages. This management system has maximized opportunity and flexibility for hunters while simplifying regulations and enforcement. In the 30-plus years since implementation, Region 7 has seen a reduction in game damage complaints, and an increase in buck-to-doe ratios. Mule deer populations and harvest have been stable long-term, and population fluctuations have decreased in magnitude. This harvest strategy has produced similar results in both Region 7 as a whole (75% private lands) and on the Custer National Forest, a 436,000-ac block of public land
Investigating Hydrologic Alteration as a Mechanism of Fish Assemblage Shifts in Urbanizing Streams
Stream biota in urban and suburban settings are thought to be impaired by altered hydrology; however, it is unknown what aspects of the hydrograph alter fish assemblage structure and which fishes are most vulnerable to hydrologic alterations in small streams. We quantified hydrologic variables and fish assemblages in 30 small streams and their subcatchments (area 8-20 km 2) in the Etowah River Catchment (Georgia, USA). We stratified streams and their subcatchments into 3 landcover categories based on imperviousness (20% of subcatchment), and then estimated the degree of hydrologic alteration based on synoptic measurements of baseflow yield. We derived hydrologic variables from stage gauges at each study site for 1 y (January 2003-2004). Increased imperviousness was positively correlated with the frequency of storm events and rates of the rising and falling limb of the hydrograph (i.e, storm flashiness ) during most seasons. Increased duration of low flows associated with imperviousness only occurred during the autumn low-flow period, and this measure corresponded with increased richness of lentic tolerant species. Altered storm flows in summer and autumn were related to decreased richness of endemic, cosmopolitan, and sensitive fish species, and decreased abundance of lentic tolerant species. Species predicted to be sensitive to urbanization, based on specific life-history or habitat requirements, also were related to stormflow variables and % fine bed sediment in riffles. Overall, hydrologic variables explained 22 to 66% of the variation in fish assemblage richness and abundance Linkages between hydrologic alteration and fish assemblages were potentially complicated by contrasting effects of elevated flows on sediment delivery and scour, and mediating effects of high stream gradient on sediment delivery from elevated flows. However, stormwater management practices promoting natural hydrologic regimes are likely to reduce the impacts of catchment imperviousness on stream fish assemblages. ?? 2005 by The North American Benthological Societ
Markov dynamic models for long-timescale protein motion
Molecular dynamics (MD) simulation is a well-established method for studying protein motion at the atomic scale. However, it is computationally intensive and generates massive amounts of data. One way of addressing the dual challenges of computation efficiency and data analysis is to construct simplified models of long-timescale protein motion from MD simulation data. In this direction, we propose to use Markov models with hidden states, in which the Markovian states represent potentially overlapping probabilistic distributions over protein conformations. We also propose a principled criterion for evaluating the quality of a model by its ability to predict long-timescale protein motions. Our method was tested on 2D synthetic energy landscapes and two extensively studied peptides, alanine dipeptide and the villin headpiece subdomain (HP-35 NleNle). One interesting finding is that although a widely accepted model of alanine dipeptide contains six states, a simpler model with only three states is equally good for predicting long-timescale motions. We also used the constructed Markov models to estimate important kinetic and dynamic quantities for protein folding, in particular, mean first-passage time. The results are consistent with available experimental measurements
Clarifying Some Remaining Questions in the Anomaly Puzzle
We discuss several points that may help to clarify some questions that remain
about the anomaly puzzle in supersymmetric theories. In particular, we consider
a general N=1 supersymmetric Yang-Mills theory. The anomaly puzzle concerns the
question of whether there is a consistent way to put the R-current and the
stress tensor in a single supercurrent, even though in the classical theory
they are in the same supermultiplet. As is well known, the classically
conserved supercurrent bifurcates into two supercurrents having different
anomalies in the quantum regime. The most interesting result we obtain is an
explicit expression for the lowest component of one of the two supercurrents in
4-dimensional spacetime, namely the supercurrent that has the energy-momentum
tensor as one of its components. This expression for the lowest component is an
energy-dependent linear combination of two chiral currents, which itself does
not correspond to a classically conserved chiral current. The lowest component
of the other supercurrent, namely, the R-current, satisfies the Adler-Bardeen
theorem. The lowest component of the first supercurrent has an anomaly that we
show is consistent with the anomaly of the trace of the energy-momentum tensor.
Therefore, we conclude that there is no consistent way to put the R-current and
the stress tensor in a single supercurrent in the quantized theory. We also
discuss and try to clarify some technical points in the derivations of the
two-supercurrents in the literature. These latter points concern the
significance of infrared contributions to the NSVZ beta-function and the role
of the equations of motion in deriving the two supercurrents.Comment: 22 pages, no figure. v2: minor changes. v3: sections re-organized.
new subsections (IVA, IVB) added. references adde
Whose Tweets are Surveilled for the Police: An Audit of Social-Media Monitoring Tool via Log Files
Social media monitoring by law enforcement is becoming commonplace, but
little is known about what software packages for it do. Through public records
requests, we obtained log files from the Corvallis (Oregon) Police Department's
use of social media monitoring software called DigitalStakeout. These log files
include the results of proprietary searches by DigitalStakeout that were
running over a period of 13 months and include 7240 social media posts. In this
paper, we focus on the Tweets logged in this data and consider the racial and
ethnic identity (through manual coding) of the users that are therein flagged
by DigitalStakeout. We observe differences in the demographics of the users
whose Tweets are flagged by DigitalStakeout compared to the demographics of the
Twitter users in the region, however, our sample size is too small to determine
significance. Further, the demographics of the Twitter users in the region do
not seem to reflect that of the residents of the region, with an apparent
higher representation of Black and Hispanic people. We also reconstruct the
keywords related to a Narcotics report set up by DigitalStakeout for the
Corvallis Police Department and find that these keywords flag Tweets unrelated
to narcotics or flag Tweets related to marijuana, a drug that is legal for
recreational use in Oregon. Almost all of the keywords have a common meaning
unrelated to narcotics (e.g.\ broken, snow, hop, high) that call into question
the utility that such a keyword based search could have to law enforcement.Comment: 21 Pages, 2 figures. To to be Published in FAT* 2020 Proceeding
Pomeron in diffractive processes and at large Q^2: the onset of pQCD
We study the reactions and
at large Q^2 and and small
momentum transfer, , to the nucleon where the pomeron exchange
dominates. At large Q^2 the virtual photon selects a hard pair, thus
selecting the hard pomeron component (the BFKL pomeron). The amplitudes for
both transverse and longitudinal polarizations of the initial photon and
outgoing -meson (photon) are calculated in the framework of the BFKL
pomeron exchange. Our calculations show that one cannot expect the early onset
of the pure perturbative regime in the discussed diffractive processes: the
small interquark distances, fm, start to dominate not
earlier than at in
and in
.Comment: 20 pages, LaTeX, epsfig.st
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